The ion-sensitive elements, which are present in the form of chips, must, in order to realize their purpose, be mounted such that they can, on the one hand, be subjected to the usually highly corrosive samples, without that, on the other hand, corrosion-susceptible components, such as conductive traces, come in contact with the media. To this end, the ion-sensitive element of a semiconductor chip is usually arranged aligned with an opening in a wall of a sample chamber, with an annular seal being arranged between the wall of the sample chamber and the semiconductor chip. The annular seal surrounds the opening, so that the ion-sensitive region of the semiconductor chip can be subjected to the sample, without the sample being able to reach the areas of the chip outside of the ion sensitive region.
The electric contacting of the chip proves, however, to be difficult. The state of the art uses essentially three approaches. Benton discloses in U.S. Pat. No. 5,833,824 a pH-sensor, in which an ISFET chip is secured on the underside of a substrate by means of a metal seal, which surrounds the ion-sensitive region of the ISFET chip, with the ion-sensitive region being aligned with an opening in the substrate. Outside of the region surrounded by the seal, conductive traces on the surface of the chip extend to contact surfaces, which are connected via solder or weld connections with complementary contact surfaces on the underside of the substrate. The solution proposed by Benton is very expensive in the respect that both during the manufacture of the seal and also during the effecting of the electrical contacting, expensive soldering and/or welding processes are required.
The state of the art discussed in Benton describes ISFET sensors, in which an ordinary polymeric seal is arranged about the opening of the sample chamber wall between the substrate and the ion-sensitive region of the ISFET chip. The contacting of the ISFET chip occurs, however, not to the substrate, in the sense of Benton, but, instead, to a support, which supports the ISFET chip on the rear side facing away from the substrate. To this end, bond wires are extended between contact surfaces on the front side of the ISFET chip to contact surfaces on the support outside of the bearing surface of the ISFET chip. Even this solution is expensive, because solder work is required for contacting the chip and because, in order to assure the functioning and integrity of the sensor, the chip must be placed within narrow tolerances with respect both to the substrate and the support.
Additionally, solutions are known, in which the chips have their contact surfaces, or bond pads, on the rear side facing away from the ion-sensitive region. These chips can then be contacted on the rear side via a support having complementary contact surfaces, wherein, for assuring sufficient, galvanic contacts between the rear side of the chip and the support, an anisotropic, elastic conductor, e.g. a silicone film with embedded gold filaments, is arranged in a direction perpendicular to the plane of the film.
This solution is very costly with respect to leading of the electrical contacts through the chip from its front side to its rear side increases its manufacturing costs several times.